The present invention generally relates to an electrostatic latent image developing apparatus for use in developing an electrostatic latent image formed on a surface of an electrostatic latent image carrier such as in an electrophotographic process or the like and, more particularly, to a reference value setting means for an automatic toner concentration control device used therein.
In general, in an electrostatic latent image developing apparatus of a type utilizing a two-component developer mix comprised of a toner powder and a magnetizeable carrier material, the toner powder has to be replenished in a quantity necessary to compensate for the consumption of the toner powder used for the development of latent images.
In view of the necessity of toner replenishment, various types of automatic toner concentration control devices have hitherto been proposed. For example, the Japanese Laid-open Patent Publication No. 51-47435 discloses the one which is so constructed that, when the concentration of the toner powder in the developer mix detected within the developing apparatus and subsequently compared with a reference value corresponding to a predetermined reference toner concentration is lower than the reference value, a toner replenishing means can be operated to replenish the toner powder.
The prior art automatic toner concentration control device of the type described above has been found having the following problem. While a reference value for a toner concentration detecting means and that for a toner replenishment control means had been fixed prior to the shipment from the factory, it often occurs that the fine adjustment and/or the re-setting thereof are required at the time of installation of a copying machine and/or at the time of subsequent replacement of the developer mix. This is because a detection output of the toner concentration detecting means changes subtly depending on the environment in which the copying machine is placed and/or the characteristics of the newly replaced developer mix.
Since the fine adjustment and/or the re-setting referred to above are performed by a servicing engineer in such a way as to turn a potentiometer on the toner concentration detecting means and/or a reference value regulator while the copying machine is being operated, that is, since the fine adjustment and/or the re-setting are carried out by a servicing engineer using his head, not only is the procedure complicated, but also the extent to which they are performed varies from one servicing engineer to another, and therefore, they cannot be always accurately performed.